Camera exposure control



United States Patent Inventor Gerald Lee Jenkins Rochester, New York Appl. No. 746,687

Filed July 22, 1968 Patented Nov. 3, 1970 Assignee Eastman Kodak Company Rochester, New York a corporation ot' New Jersey CAMERA EXPOSURE CONTROL 9 Claims, l Drawing Fig.

U.S. Cl. 95/64, 95/10, 352/72, 352/141 Int. (`l G03b 7/08, G03b 19/18 -Field olSearch 352/141,

[56] References Cited UNITED STATES PATENTS 3,312,158 4/1967 MacMillin etal B52/78X 3,3 114,344 4/1967 Annyl et al. 352/72X 3,444,798 5/1969 Mayr et al 352/141X Primary Examiner-Norton Ansher Assistant Exam iner-Joseph F. Peters, Jr. Attorneys- Robert W. Hampton and Daniel E. Sragow ABSTRACT: In order to avoid underexposure when photographing scenes having high background illumination with film having relatively low sensitivity, the minimum exposure is controlled, in an automatic exposure control, in response to the film sensitivity coding on a film cartridge. A film speed notchsensing member senses a notch on the film cartridge which is l indicative of the speed of the film contained therein. The

above member controls a movable stop member which in turn limits the diaphragm blade movement which is automatically positioned by an exposure control circuit.

Patented'. N0v.3,1 97o Y f 3,537,374.. Y

GERALD L. JENKINS v INVENTOR- BY @M/f u ATTORNEY CAMERA EXPOSURE CONTROL BACKGROUND OF THE INVENTION l. Field of the Invention The present invention relates to film-cartridge-loaded cameras of the type having automatic exposure control systems incorporated therein. More particularly, this invenresponds is generally arranged in the camera housing so as to view the subject matter of interest through a relatively large field stop, or alternatively, through a wide-angle lens. The basic reason for this arrangement stems simply from the fact that the sensitivity of conventional nonsophisticated photosensitive elements of the type adapted for use in moderately priced cameras is insufficient to permit acceptable system performance when the field of view is comparatively narrow. In other words the low sensitivity of the photosensitive element indicates the use of a wide fieldof view in order that a greater amount of lightmay be directed on the element so as to raise its electrical response tov an operable level.

Generally the subject matter of photographic interest coinprises only a small portion of the field of view ofthe exposure control system. Since the photosensitive element in such a system is usually not provided with means for discriminating between background and subject brightness, the light issuing from all portions of the field of view becomes integrated. by the photosensitive element and an output isl provided which is merely representative of the average scene brightness, of the entire field of view of the system. As is readily apparent, when the background and subject are of comparable brightness, both will be properly exposed in the photographic record. However, when there is a substantial difference between background and subject brightness, the former tends, to overshadow the latter due to its relative size, thereby causing the exposure control system tol be fooled and thus produce an output more representative of the background brightnessl than subject brightness.

It is well known, from empirical data, that the field brightness of common subjects of photographic interest rarelyL exceeds a value of approximately 2,000 foot-lamberts, even-y under the brightest natural lighting conditions, Thus, using this value inthe standard exposure equation,

brightness (2,000 foot-lamberts) may be readily computed-'as` a function of film speed. For instance, assuming an exposure:

time of one thirtieth second and an exposureconstant of 4.75 (a reasonable average value for conventional exposure control systems), the minimum aperture size to which the/picture-taking lens must befreducedso as to properly-.exposetilm of ASA 25 to the maximum subject brightness isf/ 19. Similarly, when film of ASA 100 is employed, the minimumaperturesizemay be computed to be f/36, assumingthe same exposuretimeand exposure constant.

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the maximum anticipated brightness of the subject of interest.

On some occasions, such as when the sun isreflected or is shining directly into the field of view of the exposure control system, the brightness of the background will far exceed 2,000 foot-lamberts and thereby cause the averagebrightness of the entire field of view to be in excess of 2,000 foot-lamberts. On such occasions, the exposure control systems will tend to reduce the aperture of the picture-taking lens below the size necessary to properly expose the subject of interest, thereby resulting in an underexposure of such subject. Such underexposure is obviously undesirable.

SIMMARY OF THE INVENTION In accordance with the present invention a mechanism is provided which automatically prevents the exposure control system from reducing the size of the picture-taking lens below that minimum value which will produce proper exposure of film of a specific film speed at the maximum anticipated subject brightness. The mechanism is designed so as to be responsive to the notch encoding on film cartridges which is indicative ofthe speed of the film contained thereby.

It is, therefore, an object of the invention to provide a means for preventing underexposure of subjects of photographic interest when the background against which such subjects are situated is of a brightness substantially in excess of Another object of this invention is to provide a camera mechanism, operable in response to the film speed notch encoding on film cartridges, for overriding the output of a camera exposure control system when the average scene brightness detected by such system exceeds a predetermined maximum value.`

Other objects of the invention will be apparent from the following'description with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a perspective view of a camera housing in phantom showing a camera mechanism and a coded film carj tridge according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, a camera has a picture-taking lens I0, exposure control system l5, and chamber means 20 for receiving a film cartridge 25. Basically, the exposure control system lS-comprises an exposure meter 16 (shown schematically)k which is operably controlled by a photosensitive element 17, and a diaphragm vane 18 which is pivotally coupled with the exposure meter 16 and is movable in accordance with the quantity of light-striking photosensitive element I7. Diaphragm vane 18 is provided with an elongated tapered aperture 19 which is arranged on the optical axis of lens l0 so as tovary the amount of light passing through lens l0 in accordance with the level of field brightness. Film cartridge 25 is provided'with aperture 26fthrough which film may be exposed' to light passing through lens. l0, and is further provided with' notch encodings 27, 28. which are. indicative of the speed and spectral sensitivity, respectively, ofthe particular film contained by the cartridge. Generally notch 27 varies in length between cartridges depending on the speed of the film contained therebyy and the presence or absence of notch 28 is indicative of the spectral sensitivity of the film, the'notch being present when the film contained'by cartridge I2 is of the type adapted to be exposed to artificial light.

Basically, the invention comprises. al film speed notchsensing member 30 and amovable stop member 40. Notchsensingmember 30 is pivotally mounted to the camera housingon shaft 3l and is biased by spring 32 to rotate thereabout in a counterclockwise direction 'toward cartridge chamber 20. Anabutment (not shown) is provided for positioning member 30. as shown inthe drawing. Notch-sensing member 30 is proarranged to cooperate with film speed-notch coding27, and a perpendicularly extending lug 34. Stop member 40 is pivotally mounted to the camera housing on shaft 41 and is provided with a pair of laterally extending arms 42 and 43 which are srranged to cooperate with lug 34 of member 30 and with lug 18a of diaphragm vane 18, respectively. Arm 42 is provided with a lug 42a which is arranged to interact with lug 34 when notch-sensing member 30 is caused to pivot in a clockwise direction by cartridge 25. By this arrangement, stop member 40 is caused to pivot in a counterclockwise direction about shaft 4l when cartridge 25 contains film havinga speed which requires the movement of diaphragm vane 18 to be limited so as to provide proper exposure when a subject of maximum brightness is to be photographed. Arm 43 is provided with an upper extension 43a which is arranged to engage lug 18a of diaphragm vane 18, and thereby stop the pivotal movement of diaphragm vane 18 in such a position as to provide the desired minimum exposure aperture for the particular speed film being used.

The invention operates in the manner hereinafter described.

When film cartridge 25 contains film having a speed which requires the output of the exposure control system to be overridden, notch 27 will be of a length, which precludes entrance therein of notch feeler 33. As cartridge 25 is inserted into the -camera cartridge chamber 20, notch feeler 33 will abut the forward face of cartridge 25 and thereby impart aclockwise pivotal movement in notch-sensing member 30. This moveinent causes lug 34 to engage lug 42a of stop member 40 which, in turn, imparts a counterclockwise movement instop member 40. Subsequent to such counterclockwise movement, stop member 40 is caused to come to rest in a position such that the upper extension 43a thereof is in the path of travel of lug 18a of diaphragm vane 18. Thus, when the average field brightness exceeds the maximum anticipated level of subject brightness, lug 18a will impinge upon extension 43a and come to rest.v By this arrangement, `the output of the exposure control system is overridden and the aperture size of lens is prevented from being reduced to a level which would result in underexposure of the subject matter of interest. When car tridge notch 27 is of a size indicative of a lm speed which does not require thev use of stop member 40, notch feeler 33 will be permitted to enter notch 27 and thereby permit members 30 and 40 to remain in the position shown. In this position diaphragm vane 18 is free to pivot over its maximum range, and thereby reduce the f/number of taking lens l0 to a value governed by the extreme tapered end of aperture 19.

The invention has been described in considerable detail with particular reference to a preferred embodiment thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

lclaim:

1. ln a photographic camera having means for forming an image of a scene on a photosensitive surface and means for receiving a film cartridge having a tactile discontinuity thereon representative of film speed, the combination coniprising:

a. an exposure control device having a light-sensitive member disposed for illumination by light from said scene and having a diaphragm vane movable under control of said light-sensitive member to any of a plurality of positions as ay function of the brightness of said scene, said vane having an elongated tapered aperture therein movable relative to said image-forming means for regulating the admission of scene light to said photosensitive surface; and

b. means responsive to the lm cartridge discontinuity for limiting movement of said diaphragm vane relative to said image-forming means so as to prevent further attenuation of scene light reaching said photosensitive surface when said scene light exceeds a predetermined maximum value.

2. The invention according to claim 1 wherein said means for limiting movement of said diaphragm vane comprises a movably mounted discontinuity-sensing member which is biased by spring means toward a first position engaging said tridge discontinuity when'the cartridge is received by saidv chamber means.

4. The invention according to claim 3 wherein said means' for limiting movement of said diaphragm vane further comprises a movably mounted stop member arranged to engage said discontinuity-sensing member when the latter is caused to pivot by the film cartridge discontinuity, thereby causing said stop member to be moved into the path of pivotal movement of said diaphragm vane so as to prevent further attenuation of scene light reaching said photosensitive surface when said scene light exceeds a predetermined value.

5. A camera comprising:

a. a picture-taking aperture;

b. an exposure control system including means for varying the size of said picture-taking aperture over a predetermined range of aperture sizes in accordance with scene brightness;

c. means for receiving a film cartridge having a tactile discontinuity thereon representative of the speed of the film contained thereby; and

d. means responsive to said film cartridge discontinuity for varying the range over which said picture-taking aperture may be varied. v

6. The invention according to claim 5 wherein:

a. the means for varying said aperture size comprises a diaphragm vane having an elongated tapered aperture therein, said vane being movably mounted so as to permit movement of said tapered aperture relative to said picture-taking aperture whereby said picture-taking aperture size may be varied in accordance with field brightness; and

b. said means for varying the range over which said picture- 4taking aperture may b'e varied comprises discontinuitysensing means movable into the path of movement of said diaphragm vane in response to a selected film speed discontinuity whereby the range over which said diaphragmvane may vary said picture-taking aperture size is limited when thev average field brightness of the scene of photographic interest exceeds a predetermined value.

7. A camera comprising:

a.rmeans for receiving a film cartridge which has a tactile discontinuity a dimension of which is representative of the sensitivity of the film contained therein;

b. an exposure control which varies the exposure of the film in accordance with scene illumination, said exposure control being operable in a certain range;

c. means for sensing said dimension of said tactile discon tinuity of the cartridge; and.

d. meansicoupled to said sensing means for varying the range of said exposure control in response to a predeter-v mined dimension of the tactile discontinuity.

8. A camera comprising:

a. means for receiving a film cartridge which has a tactile discontinuity a dimension of which is representative of the sensitivity of the film contained therein;

b. an exposure control which is adapted to vary exposure of the film in accordance with scene illumination, said exposure control including variable means for preventing said exposure control from attenuating exposure of the film below a predetermined minimum;

c. means for sensing said dimension of said tactile discontinuity of the cartridge; and

d. means coupled to said sensing means for varying said preventing means in response to a predetermined dimension of the tactile discontinuity.

v9. ln a` camera having an objective for forming an image of a scene in a primary image .plane and means for receiving a iilm cartridge for locating lm in the cartridge substantially in the primary image plane, the film cartridge having indicia representative of lm speed, the combination comprising:

a. an exposure control apparatus including a photoresponsive member disposed for illumination by light from a scene, and having an adjustable exposure control member movable under control of the photoresponsive member for variably attenuating the amount of scene light trans- 

